Elastic client interface for tunable optical transponder

ABSTRACT

There are provided an optical transponder having a first end and a second end, as well as an electric switch having the transponder. The transponder includes an optical interface, at the first end, having a variable rate optical transmitter and a variable rate optical receiver to respectively transmit and receive signals using at least one of different bandwidths and different bit rates. The transponder further includes an electrical interface, at the second end, having an electrical interface throughput matching an optical capacity of the optical interface. The transponder also includes a processor for controlling the optical capacity.

RELATED APPLICATION INFORMATION

This application claims priority to provisional application Ser. No.61/808,941 filed on Apr. 5, 2013, incorporated herein by reference.

BACKGROUND

1. Technical Field

The present invention relates to signal processing, and moreparticularly to an elastic client interface for a tunable opticaltransponder.

2. Description of the Related Art

Recent technology innovations in optical transponders have enabled thegeneration of a flexible modulation format and symbol rate, which leadsto flexible bandwidth usage. Innovations in optical switches haveenabled gridless optical spectrum switching which means the flexibleselection of any frequency and any bandwidth. These innovationscontribute to the paradigm of an elastic network, allowing serviceproviders to satisfy the network's increasing needs without excessiveinvestment.

An ideal elastic network requires one more feature to fully reflect thenetwork needs: the spectrum usage shall be adaptive to the trafficcapacity, not just the interface rate. However, the current interfaceswith client networks are mostly fixed rate, and to ensure no trafficloss, the core network side of the optical transponder matches thatfixed rate, irrespective of the actual throughput. This problem blocksthe possibility to further reduce spectral utilization.

FIG. 1 shows a network environment 100 with fixed rate client interfaces111, 112, and 113, in accordance with the prior art. The networkenvironment 100 includes a flexgrid all-optical network 120, clientnetworks 131 and 132, optical transponders 141, 142, 143, and 144, andthe fixed rate client interfaces 111, 112, and 113. Disadvantageously,the client interfaces 111, 112, and 113 are fixed rate.

SUMMARY

These and other drawbacks and disadvantages of the prior art areaddressed by the present principles, which are directed to an elasticclient interface for a tunable optical transponder.

According to an aspect of the present principles, there is provided anoptical transponder having a first end and a second end. The transponderincludes an optical interface, at the first end, having a variable rateoptical transmitter and a variable rate optical receiver to respectivelytransmit and receive signals using at least one of different bandwidthsand different bit rates. The transponder further includes an electricalinterface, at the second end, having an electrical interface throughputmatching an optical capacity of the optical interface. The transponderalso includes a processor for controlling the optical capacity.

According to another aspect of the present principles, there is providedan electric switch. The electric switch includes an optical transponderhaving a first end and a second end. The optical transponder includes anoptical interface, at the first end, having a variable rate opticaltransmitter and a variable rate optical receiver to respectivelytransmit and receive signals using at least one of different bandwidthsand different bit rates. The optical transponder further includes anelectrical interface, at the second end corresponding to a fabric sideof the electric switch, having a fabric side throughput matching anoptical capacity of the optical interface. The optical transponder alsoincludes a processor for controlling the optical capacity.

These and other features and advantages will become apparent from thefollowing detailed description of illustrative embodiments thereof,which is to be read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

The disclosure will provide details in the following description ofpreferred embodiments with reference to the following figures wherein:

FIG. 1 shows a network environment 100 with fixed rate client interfaces111, 112, and 113, in accordance with the prior art;

FIG. 2 shows an exemplary network environment 200 to which the presentprinciples can be applied, in accordance with an embodiment of thepresent principles;

FIG. 3 shows an exemplary optical transponder 300, in accordance with anembodiment of the present principles;

FIG. 4 shows a method 400 for flow control, in accordance with anembodiment of the present principles;

FIG. 5 shows a method 500 to increase bandwidth based on detected burstlength, in accordance with an embodiment of the present principles;

FIG. 6 shows a method 600 to increase bandwidth based on opticaltransmitter burst length and XON/OFF status, in accordance with anembodiment of the present principles;

FIG. 7 shows a method 700 to increase bandwidth based on opticaltransmitter burst length and XON/OFF status, in accordance with anembodiment of the present principles; and

FIG. 8 shows an integrated switch architecture 800, in accordance withan embodiment of the present principles.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present principles are directed to an elastic client interface for atunable optical transponder.

FIG. 2 shows an exemplary network environment 200 to which the presentprinciples can be applied, in accordance with an embodiment of thepresent principles. The network environment 200 includes awavelength/optical-spectrum switched network (hereinafter “opticalnetwork” in short) 202, electrically switched networks (also referred toherein as “client networks”) 204 and 206, optical network controller213, optical interface control channels 208 and 210, tunable opticaltransponders 212 and 214, optical path control channels 216, 218, and220, and switches 222, 224, and 226.

FIG. 3 shows an exemplary optical transponder 300, in accordance with anembodiment of the present principles. The optical transponder 300 canbe, for example, any of optical transponders 212 and 214. The opticaltransponder 300 includes a physical interface 302 to the client networks(e.g., networks 204 and 206), and a client side packet/frame processor304.

In the direction from a client network (e.g., networks 204 and 206) tothe optical network 202, the optical transponder 300 further includes avariable rate electrical signal generator 306A and a variable rateoptical modulator 308A. The electrical signal generator 306A can be, forexample, a digital signal processor (DSP) and so forth. In the directionfrom the optical network 202 to a client network (e.g., networks 204 and206), the optical transponder 300 further includes a variable rateoptical receiver 306B and a variable rate signal demodulator 308B. Thesignal demodulator 308B can be, for example, a digital signal processor(DSP) and so forth.

While shown separately, in other embodiments, the functions of thesignal generator 306A and modulator 308A can be combined into a singleparticular element, and the functions of the optical receiver 306B andthe demodulator 308B can be combined into a single given element, wherethe particular element and the given element are the same element (e.g.,an optical transceiver) or different elements. Hence, the signalgenerator 306A and the modulator 308A are also collectively referred toherein as “an optical transmitter” in short, while the optical receiver306B and the demodulator 308B are also collectively referred to hereinas “an optical receiver” in short. These and other variations of theelements of FIG. 3 are readily determined by one of ordinary skill inthe art given the teachings of the present principles provided herein,while maintaining the spirit of the present principles.

Reference will now be made to FIGS. 2 and 3. The present principles arerelated to a tunable optical transponder (e.g., optical transponders 212and 214) which works as the bridge between an electrically switchednetwork (networks 204 and 206) and an optical network 202. For thedirection from the electrical network 202 to an optical network (e.g.,networks 204 and 206), a transponder has the signal generator 306A(including a transmission related electrical processor 361) and theoptical modulator 308A to convert the signal to the format suitable forWDM (wavelength division multiplexing) switching (via switches 222, 224,and/or 226) and transmission. For the direction from the optical network202 to an electrical network (networks 204 and 206), the opticalreceiver 308B and demodulator 306B (including a reception relatedelectrical processor 371) demodulate the received optical signal, andconvert the received signal back to the format required by theelectrical network (networks 204 and 206). The optical transceiver hasthe capability to adjust the modulation format, bit rate, and signalbandwidth, to adapt to the requirement of spectrum usage, transmissioncapacity, and signal quality. The interface 302 to the client network isin communication with processor 304 with the capabilities of adapting tothe optical data rate, and/or estimating the required traffic capacity,to match the capacity between the client networks 204 and 206 and theoptical network 202. The physical interface 302 to the client network204 and 206 can be either optical or electrical. The optical interfacehas the channel to communicate with the optical network controller 213(such as channel 208 and 210), which can modify the optical path (e.g.,through control paths 216, 218, and 220) to meet the bandwidthrequirement. In an embodiment, the transmission related electricalprocessor 361 and the reception related electrical processor 371 can bethe same processor or different processors. In an embodiment, the clientside processor 304 can be the same processor as transmission relatedelectrical processor 361 and/or the reception related electricalprocessor 371.

A description will now be given of a first embodiment directed to usingflow control to regulate client traffic, and allocating optical capacitybased on an estimated throughput request.

Assume the client interface 302 has a flow control feature, which meansthe transaction can be disabled by sending XOFF and enabled by sendingXON. Electrical processor 304 has a buffer 388 that is able to tolerantthe reaction delay when XOFF is sent, and to avoid traffic underflowwhen XON is sent. Whenever the buffer usage is above threshold 1 (TH₁),processor 304 sends XOFF to the connected client equipment; whenever thebuffer usage is below threshold 2 (TH₂, where TH₁>TH₂), 304 sends XON toenable traffic receiving. The client rate regulation is actuallydetermined by the optical transmission rate because the readout rate ofthe buffer 388 of the processor 304 cannot exceed the optical capacity.Note that TH₂ may be dynamically adjusted based on allocated opticalcapacity. This method is shown in FIG. 4.

FIG. 4 shows a method 400 for flow control, in accordance with anembodiment of the present principles. At step 410, check the bufferstatus. At step 420, determine whether the buffer usage is larger thanTH₁ or less than TH₂. If the buffer usage is larger than TH₁, then themethod continues to step 430. If the buffer usage is smaller than TH₂,then the method continues to step 450. If the buffer usage is not largerthan TH₁ or smaller than TH₂, then the method returns to step 410.

At step 430, determine whether the current state is XON. If so, then themethod continues to step 440. Otherwise, the method returns to step 410.

At step 440, send XOFF to the client network, and return to step 410.

At step 450, determine whether the current state is XOFF. If so, thenthe method continues to step 360. Otherwise, the method returns to step410.

At step 460, send XON to the client network.

On the other hand, optical transmission capacity shall be adjusted basedon client traffic throughput, to provide enough pipe and avoid trafficcongestion. This is achieved by monitoring or estimating the trafficthroughput and allocating the needed optical capacity accordingly. Thereare two scenarios to consider: to increase capacity when traffic volumegoes higher; and to decrease capacity when traffic volume goes lower.

A description will now be given relating to traffic volume going higher.When overall traffic volume is higher than optical capacity, processor304 will frequently send XOFF (and then XON when buffer 388 is belowTH₂) to its connected client. However, this may somehow be confused withthe case of burst traffic. For example, if the current burst is a shortburst that is treated as a higher bandwidth need, it may result in underusage of the optical spectrum and/or too frequent capacity adjustmentwhich may overhaul the capability of the controller (e.g., controller213). Moreover, if the traffic amount increase is treated as a burst andan increasing-bandwidth request is not sent promptly, it may affect thenetwork throughput or cause longer traffic delay. One embodimentinvolves defining the burst length threshold BL₁. Transponder monitorsthe receiving traffic burst length BT, which is counted from the time itsends XON following an XOFF, to when it encounters a silent period inthe receiving link while the state is XON. If BT is longer than BL₁, itis considered that the traffic amount is larger than the current opticalpipe capacity, so the request to increase optical capacity shall besent. This method is shown in FIG. 5.

FIG. 5 shows a method 500 to increase bandwidth based on detected burstlength, in accordance with an embodiment of the present principles. Themethod includes a burst length calculation branch 551 and a bandwidthrequest branch 552. Steps 510, 520, 530, 540, and 550 pertain to theburst length calculation branch 551. Steps 560, 570, and 580 pertain tothe bandwidth request branch 552.

At step 510, start a timer. At step 520, check the client interfacereceiving status. At step 530, determine if the client interface 302 isidle. If so, then the method continues to step 540. Otherwise, themethod returns to step 520.

At step 540, determine if current state is XON. If so, then the methodcontinues to step 550. Otherwise, the method returns to step 520.

At step 550, reset the timer, and return to step 510.

At step 560, determine if the burst length (timer_value*rate) is lessthan BL₁. If so, then the method continues to step 570. Otherwise, themethod returns to step 560.

Alternatively, the burst length is defined as the period PL that clientinterface processor 304 keeps the electrical signal generator 306A andoptical modulator 308A fully loaded; in case PL>BL₁ and XOFF is sent, itis considered as increased traffic volume, so optical capacity shall belarger. This method is shown in FIG. 6.

FIG. 6 shows a method 600 to increase bandwidth based on opticaltransmitter burst length and XON/OFF status, in accordance with anembodiment of the present principles. The method includes a transmitteridle monitoring branch 651 and a bandwidth request branch 652. Steps610, 620, and 630 pertain to the transmitter idle monitoring branch 651.Steps 640, 650, 660, and 670 pertain to the bandwidth request branch652.

At step 610, start a timer. At step 620, determine whether thetransmitter is idle. If so, then the method continues to step 630.Otherwise, the method returns to step 620.

At step 630, reset the timer, and return to step 610.

At step 640, determine whether XOFF was sent. If so, then the methodcontinues to step 650. Otherwise, the method returns to step 640.

At step 650, determine whether timer (timer_value) is less than BL₁. Ifso, then the method continues to step 660. Otherwise, the method returnsto step 640.

At step 660, issue a request for more bandwidth. At step 670, reset thetimer, and return to step 640.

Note that for such case, BL₁ can be modified whenever optical capacityis adjusted. The step size of optical capacity adjustment shall considerabnormal conditions such as, for example, a drastic increase of trafficvolume to the maximum link capacity. It shall be the result of allowedresponse time (i.e., from the time traffic volume increases, to the timethe link capacity shall be settled to accommodate the increase),capacity adjustment (i.e., maximum optical capacity minus the currentallocated capacity), the path responding speed, and allowed requestfrequency (how many requests are allowed in one second—this is thenumber to avoid controller overhauling). The preceding are merelyillustrative and, thus, other criteria or variation of the precedingcriteria can also be used in accordance with the teachings of thepresent principles, while maintaining the spirit of the presentprinciples.

A description will now be given relating to traffic volume going lower.When traffic volume goes lower, client processor 304 will encounter anidle period in sending data to signal generator 306A. Unlike the casewhen traffic volume goes higher, here the slow response will not causetraffic congestion or extra delay. Thus, one embodiment is to monitorthe traffic before taking any action. Traffic can be characterized asaverage throughput, burst case throughput, and burst length. Opticalcapacity adjustment can be done based on a pre-configured policy suchas, for example, (1+x)*average_throughput where x is the speedup. Theburst length threshold BL₁ given above can be updated based on amonitoring result as well, to better reflect the actual traffic pattern.Alternatively, optical capacity is reduced step by step by level C_(r),when the average of monitored unused capacity is larger than C_(r).

During system initialization, the allocated optical capacity can be atits maximum, or based on pre-knowledge or client network policysettings. The high-level method is shown in FIG. 7.

FIG. 7 shows a method 700 to adjust bandwidth through trafficmonitoring, in accordance with an embodiment of the present principles.At step 710, allocate an initial capacity. At step 720, perform trafficmonitoring (e.g., buffer usage, average capacity, peak rate, burstlength, etc.). At step 730, perform an action based on a monitoringresult, and return to step 720.

A description will now be given of a second embodiment directed toavoiding under-allocating optical capacity.

This embodiment refers to the case that optical capacity is always (orat the best effort) set to a rate that is higher than the client trafficrate, up to its maximum capacity. Optical capacity is allocated based onthe past and predicted client traffic throughput, to avoid trafficoverflow as much as it can. The transponder continuously monitors clienttraffic, including the average throughput for time periods such as, forexample, the past hour, peak throughput within the past 5 minutes,traffic growing trend (like the curve of average throughput for each 5minutes), and burst length. Of course, the preceding time periods areillustrative and, thus, other time periods can also be used.

In one embodiment, the optical capacity is allocated with reference tothe peak throughput (TH_(p)), with some pre-defined room (ratio) forhigher tolerance, for example 1.2*TH_(p). This ratio can also beadjusted based on the past traffic growing trend, and the historicalstatistics like time of the day or day of the week.

If the client interface 302 supports flow control using XON/XOFF,whenever the queue size is above threshold TH₁, the transponder willsend XOFF; when it's below TH₂, it will send XON. This operation is sameas that described for the first embodiment.

There is also the case that the client interface 302 does not have aflow control feature. The transponder will need a large buffer 388 totolerant drastic traffic volume change and large burst size. In suchcase, if the burst can be accommodated by the available buffer 388, thecapacity to allocate will be the same as the above mentioned; otherwise,extra capacity will be needed. In one embodiment, the buffer 388 has thecapacity at least to accommodate one burst, plus the traffic volume(C_(fr)) of full-rate for request-reaction period. Given threshold TH₃,when the queue length is larger than TH₃, transponder will request forhigher optical capacity. The additional capacity to request isdetermined by the available buffer size, the client link data rate, theupcoming traffic estimation (under the given confidence), and therequest-reaction latency for capacity adjustment. In one embodiment,client link rate is R_(C), available buffer size is B_(a),request-reaction time is T_(r), the additional optical capacity that canbe allocated is C_(a), then for each request, the added bandwidth canbe, for example, C_(a)/(lowest_integer(B_(a)/(R_(c)*T_(r)))). This is toguarantee that even when the client interface 302 becomes fully loaded,there will not be traffic loss, by growing to maximum optical ratebefore the buffer 388 goes full. TH₃ shall be larger than the maximumburst length, so that burst traffic within certain range can beaccommodated without requesting for larger bandwidth. Alternatively, itmay request for highest available capacity, if consider this belongs tothe abnormal case which rarely happens. Capacity adjustment for queuelength below TH₃ still follows the same procedure as mentioned above,which is to allocate based on the monitoring result and prediction.

A description will now be given of a third embodiment directed to achannelized TDM interface, with optical capacity based on connected TDMchannels.

For a channelized TDM interface, the client link capacity can be knownbased on the established connections, and the optical capacity matchesthe total allocated channel capacity. For channels carrying packetsapplications, such as Ethernet over ODU/OPU (optical data/protocol unit)using GFP (Generic Framing Procedure), if the packets can be extractedand re-encapsulated, the capacity variation may follow the sameprocedure as mentioned in the first and second embodiments. Otherwise,it is treated the same as fixed TDM channel.

A description will now be given of a fourth embodiment directed to atransponder integrated into an electrical switch, with optical capacitybased on monitored and predicted traffic volume.

When a transponder is integrated into an electrical switch, there willbe associated queues for the transponder, so optical capacity allocationwill be the same as the second embodiment, for the particular case witha large integrated buffer 388. For a standalone transponder that is ableto get queuing information from its connected switch, it is the specialcase of the integrated solution, so the procedure will be the same aswell. It is to be appreciated that the optical transponder in accordancewith the present principles can be incorporated into switches such as,for example, switches 222, 224, and 226. FIG. 8 shows an integratedswitch architecture 800, in accordance with an embodiment of the presentprinciples. A switch 800 has line cards for client interfaces, such asline card 802 and line card 804, connecting to client networks (such asclient networks 204 and 206). The switch 800 also has line cards foroptical interfaces (such as optical line cards 806 and 808) withintegrated optical transponders, connecting to an optical network (suchas network 202). The switch 800 further has a switch fabric 810. Clientline cards 802 and 804 have a client interface 822 (equivalent tointerface 302), a client traffic processor 824, and a queuing and fabricinterface 826. Optical line cards 806 and 808 have an optical interface832 which is the simplified illustration of 306A/306B/308A/308B, atraffic processor 834, and a queuing and fabric interface 836.Function-wise, elements 826 and 836 have the same functions, andelements 824 and 834 have the same function. Queuing is either done at asource port using Virtual Output Queuing (VOQ), or at an output port.The traffic amount to the optical transponder is considered as thevolume switched from fabric 810 to that optical line card. Queue statusmonitoring is based on the corresponding VOQ or the output buffer forthe optical line card.

Thus, the present principles use several schemes to solve theaforementioned problems of the prior art.

One such scheme involves using flow control to limit the traffic ratefrom client to transponder, to match the allocated optical capacity. Ifthe rate is higher than what the transponder has allocated, it sendsback XOFF to disable traffic receiving for a while. Optical capacitymatches the monitored traffic rate; if the monitored or predictedtraffic rate is higher than the current optical capacity, thetransponder requests higher bandwidth.

The method for increasing optical capacity decision is based onmonitored burst length, which is counted from the time it sends XOFF, towhen it encounters a silent period in the receiving link while the stateis XON. If BT is longer than the burst length threshold BL₁, it isconsidered that the traffic amount is larger than the current opticalpipe, so the request to increase optical capacity shall be sent.Alternatively, the burst length is defined as the period PL that theoptical transmitter is fully loaded; in case PL is larger than theconfigured threshold BL₁ and XOFF is sent, it is considered as increasedtraffic volume, so optical capacity shall be larger.

Another scheme involves monitoring client interface traffic throughput,and adjusting optical rate accordingly. The transponder has a buffer 388for burst regulation, and to hold the excessive data while requestingbandwidth adjustment. The transponder requests higher bandwidth whenbuffer usage exceeds a pre-configured threshold.

Yet another scheme is allocating optical bandwidth/capacity based on TDMchannel capacity, in case the client interface is channelized TDM.

Still another scheme is implementing the transponder an interface on anelectrical switch. The transponder monitors the traffic throughputand/or queue length to decide the needed bandwidth, and request thedetermined amount accordingly.

Thus, the present principles advantageously enable the adaptation ofoptical spectrum with client traffic capacity, which helps to saveoptical spectrum usage, and indirectly helps to reduce powerconsumption. Higher spectrum efficiency means reduced capital expensesfor service providers.

In an embodiment, a significant aspect of the present principlesinvolves the combination of flow control (XON/XOFF), traffic statistic,and optical bandwidth modification request, to make the optical capacityclose to client traffic rate. XON/XOFF are replaced by a large buffer ifthey are not supported, and bandwidth request is also decided by queuelength in such a case, besides traffic statistics.

Embodiments described herein may be entirely hardware, entirely softwareor including both hardware and software elements. In a preferredembodiment, the present invention is implemented in software, whichincludes but is not limited to firmware, resident software, microcode,etc.

Embodiments may include a computer program product accessible from acomputer-usable or computer-readable medium providing program code foruse by or in connection with a computer or any instruction executionsystem. A computer-usable or computer readable medium may include anyapparatus that stores, communicates, propagates, or transports theprogram for use by or in connection with the instruction executionsystem, apparatus, or device. The medium can be magnetic, optical,electronic, electromagnetic, infrared, or semiconductor system (orapparatus or device) or a propagation medium. The medium may include acomputer-readable medium such as a semiconductor or solid state memory,magnetic tape, a removable computer diskette, a random access memory(RAM), a read-only memory (ROM), a rigid magnetic disk and an opticaldisk, etc.

It is to be appreciated that the use of any of the following “/”,“and/or”, and “at least one of”, for example, in the cases of “A/B”, “Aand/or B” and “at least one of A and B”, is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of both options (A andB). As a further example, in the cases of “A, B, and/or C” and “at leastone of A, B, and C”, such phrasing is intended to encompass theselection of the first listed option (A) only, or the selection of thesecond listed option (B) only, or the selection of the third listedoption (C) only, or the selection of the first and the second listedoptions (A and B) only, or the selection of the first and third listedoptions (A and C) only, or the selection of the second and third listedoptions (B and C) only, or the selection of all three options (A and Band C). This may be extended, as readily apparent by one of ordinaryskill in this and related arts, for as many items listed.

Having described preferred embodiments of a system and method (which areintended to be illustrative and not limiting), it is noted thatmodifications and variations can be made by persons skilled in the artin light of the above teachings. It is therefore to be understood thatchanges may be made in the particular embodiments disclosed which arewithin the scope and spirit of the invention as outlined by the appendedclaims. Having thus described aspects of the invention, with the detailsand particularity required by the patent laws, what is claimed anddesired protected by Letters Patent is set forth in the appended claims.

What is claimed is:
 1. An optical transponder having a first end and asecond end, the transponder comprising: an optical interface, at thefirst end, having a variable rate optical transmitter and a variablerate optical receiver to respectively transmit and receive signals usingat least one of different bandwidths and different bit rates; anelectrical interface, at the second end, having an electrical interfacethroughput matching an optical capacity of the optical interface; and aprocessor for controlling the optical capacity.
 2. The opticaltransponder of claim 1, wherein the processor is a digital signalprocessor for selectively changing at least one of a symbol rate, amodulation format, and an allocated bandwidth for transmission andreception performed by the optical interface.
 3. The optical transponderof claim 1, wherein an electrical interface throughput adjustment forthe electrical interface is based on the optical capacity.
 4. Theoptical transponder of claim 3, wherein the optical capacity isdetermined based at least one of an allocated bandwidth, an opticalchannel quality, and an optical modulation format.
 5. The opticaltransponder of claim 3, wherein the electrical interface is a packetinterface having a flow control function.
 6. The optical transponder ofclaim 3, wherein the processor has an internal buffer to adapt to avariable optical rate.
 7. The optical transponder to claim 6, whereinthe electrical interface throughput is adjusted using a flow controlfunction that sends a disabling signal for disabling packet receptionwhen a buffer usage is above a first threshold and sends an enablingsignal for enabling packet reception when the buffer usage is below asecond threshold.
 8. The optical transponder of claim 1, wherein anoptical capacity adjustment is based on the electrical interfacethroughput.
 9. The optical transponder of claim 8, wherein the opticalcapacity is adjusted by at least one of adjusting an optical modulationformat and increasing or reducing an allocated bandwidth.
 10. Theoptical transponder of claim 8, wherein the electrical interface is apacket interface, and the electrical interface throughput is determinedbased on a monitored traffic bandwidth.
 11. The optical transponder ofclaim 10, wherein an increase in the optical capacity is determinedbased on a client burst length, the client burst length calculated byaccumulating a non-stopping period from a time an enabling signal issent following a disabled packet reception phase up to a first detectiontime of receiver link silence for a receiver link coupled to the opticaltransponder.
 12. The optical transponder of claim 10, wherein theallocated bandwidth is increased when the optical interface is at anallocated maximum load for a pre-defined time period and the electricalinterface is currently in a disabled packet reception phase.
 13. Theoptical transponder of claim 10, wherein the allocated bandwidth isindirectly determined from an electrical buffer queue length.
 14. Theoptical transponder of claim 8, wherein the electrical interface is atime division multiplexing interface.
 14. The optical transponder ofclaim 8, wherein the electrical interface throughput is based on aservice agreement specifying an average symbol rate and a maximum burstlength.
 15. The optical transponder of claim 1, wherein the opticalcapacity is based on a historical maximum traffic throughput at a giventime of a given date of one of a week, a month, and a year.
 16. Theoptical transponder of claim 1, wherein the optical capacity isdetermined based on a traffic prediction.
 17. The optical transponder ofclaim 1, wherein an optical receiver capacity of the variable rateoptical receiver is set based on an optical transmitter capacity of thevariable rate optical transmitter.
 18. An electric switch, comprising:an optical transponder having a first end and a second end, wherein theoptical transponder includes: an optical interface, at the first end,having a variable rate optical transmitter and a variable rate opticalreceiver to respectively transmit and receive signals using at least oneof different bandwidths and different bit rates; an electricalinterface, at the second end corresponding to a fabric side of theelectric switch, having a fabric side throughput matching an opticalcapacity of the optical interface; and a processor for controlling theoptical capacity.
 19. The electric switch of claim 18, wherein theprocessor is a digital signal processor for selectively changing atleast one of a symbol rate, a modulation format, and an allocatedbandwidth for transmission and reception performed by the opticalinterface.
 20. The electric switch of claim 18, wherein a fabric sidecapacity adjustment for the electrical interface is based on the opticalcapacity.